The trend is going from problematic 2 strokes that require a lot of maintenance to a durable 4-stroke.
We have sold way over a thousand of the HS 142 motors and can count the warranty issues on one hand [less than 5 in 5 years]. It is normally trouble free except for 2 issues.
First and foremost the motor doesn't know when to stop revving [this is also true of the Honda GXH50].
And secondly, today's gasoline is very damaging.
Problem number one usually results in the rod snapping loose and it is over. This problem was caused by several companies offering kits with "crazy" ratios, like 25 X 1. This allowed the motors to rev beyond 9,500 RPMs when the red-line is 7800. Solution was to stop selling stupid ratios.
Problem number two, however continues to haunt all of us. It isn't just a problem with the 50 CC motors, but all small motors. While an in-line filter is good, it won't stop the residue left after the gas evaporates. My solution has been to add Gummout carburetor cleaner to about every 5th or 6th tank of gas. This seems to stop all my carburetor issues on all my EZM bikes, HF equipped bikes, and my vast Whizzer collection [over 25]. If I plan to store one and not use for a while I use STA-BIL, as I found draining the gas still allowed the residue to still form inside the carburetor. In fact I found it works better to leave some gas in the system and allow the STA-BIL to do its job.
Check to see if the flywheel key has sheared, then check valve adjustment. I don't remember the exact valve setting, but I think it is posted somewhere on this site.
Have fun,